Field of the Invention
The present invention relates to a radio receiver, and particularly to a mute control method that can be appropriately employed according to a standardized digitization technology for amateur radio.
Description of the Related Art
The standardized digitization technology for amateur radio (D-STAR: Digital Smart Technologies for Amateur Radio) proposed by the Japan Amateur Radio League aims to promote the digitization of amateur radio, and version 4.3 published in September 2004 indicates that, due to digitization, the convenience of amateur radio can be dramatically improved by transmitting not only voice, even though the main subject is voice, but also data.
When version 4.3 of the standardized digitization technology for amateur radio (hereinafter simply referred to as “the standardized technology”) was published, data from personal computers and the like was envisaged as the aforementioned data. In recent years, however, radio apparatuses are equipped with a GPS receiver, and are used for exchanging their positional data. Also, due to the widespread use of smartphones, radio apparatuses are used for transmitting images captured by a smartphone from a mountainous area or the like that is outside the service range of the smartphone.
In order to support such data transmission, the applicant of the present invention proposed the invention disclosed in JP 2006-157477A. According to this invention, one piece of data is composed of two blocks, and a mini-header is embedded in the leading part of the first half of the piece of data so that multiple kinds of data can be identified.
In particular, in cases where image data is to be transmitted, the aforementioned standardized technology version 4.3 requires that voice frames always be transmitted even when no voice call is made, and accordingly the data transmission speed is approximately 950 bps, and it takes five minutes or longer to transmit a VGA size image. Hereinafter, this data transmission mode is referred to as the “slow data” mode, for the sake of convenience. Meanwhile, occasions of transmitting image data have rapidly increased, and accordingly data transmission that requires only a short period of time is demanded.
Considering the situation above, the inventors, etc., of the present invention proposed a scheme in which voice frames are also used for the transmission of data for data communication, and version 5.0 of the standardized digitization technology for amateur radio, which includes the details of the proposed scheme, was published in August 2014. According to this scheme, the transmission speed is increased to 3.6 kbps, which is approximately four times higher than previous. Hereinafter, this data transmission mode is referred to as the “fast data” mode, for the sake of convenience.
Prior to a description of the present invention, a description is given of a method for conversion (recombination) to the fast data according to version 5.0 of the standardized digitization technology for amateur radio, on which the present invention is based, with reference to FIG. 1.
First, when a call is generated, a bit sync B, a frame sync F, and a header H, which have predetermined sizes, are transmitted, and main data D, which includes voice frames, data frames, etc., is then transmitted. The frame period of the main data D is 420 msec, and, as shown in FIG. 1, the main data D is divided into ten blocks.
Each block is basically composed of pairs of a voice frame of 72 bits (9 bytes) and a data frame of 24 bits (3 bytes). These frames are combined in this order because, as described above, voice is the main subject. Only in the first block (block number 1), the first data frame is a sync signal. For this reason, the first block includes three pairs of a voice frame and a data frame. The following blocks, namely the second to tenth blocks, each include two pairs of a voice frame and a data frame.
The frame configuration is as described above. For the sake of convenience in treating the blocks as the fast data, a voice frame and a data frame in each block are combined such that a data frame comes first and is followed by a voice frame, as shown in detail in FIG. 1. This is for the purpose of checking the mini-header embedded in the leading part of the data, and distinguishing transmission of voice signal data alone, transmission of data for data communication alone, simplified transmission of voice signal data and data for data communication at the same time, and transmission of data for data communication utilizing voice frames as well, from each other.
Regarding the first frame, note that the first voice frame combined with the sync signal is relocated to the last part. The length in time of each pair of a voice frame and a data frame is 20 msec, and accordingly the frame period of the entire main data D is 60+40×9=420 msec, as described above. The first 8 bits (1 byte) of the data frames in the first half constitute the aforementioned mini-header, and the effective data length of the first block is 224 bits (28 bytes), and the effective data length of the second to tenth blocks is 160 bits (20 bytes), respectively.
The mini-header is 8 bits (1 byte) of data, and is represented as a two-digit hexadecimal. The first digit indicates the data type, and the second digit indicates the data length (or the block number). For example, according to the standardized technology version 5.0, the first digit is 3x and the second digit is 1 to 5 (bytes) in the case of simplified transmission by which data for data communication can be transmitted as well while voice signal data is transmitted, that is, in the case of slow data transmission.
The total data length of the two data frames is 48 bits (6 bytes), but since the mini-header occupies 8 bits (1 byte), the data is the remaining 1 to 5 bytes. On the other hand, in the case of transmission of data for data communication utilizing the voice frames as well, that is, in the case of fast data transmission, the first digit is 8x or 9x, and the second digit is 1 to F (1 to 15 bytes) or 0 to C (16 to 28 bytes).
Fast data transmission is enabled in this way. However, if the data of the mini-header is garbled, there are problems such as the voice frames not being recognized as including data for data communication, and being reproduced as voice, which causes abnormal sound or noise. Specifically, garbling is caused by the mini-header having a digit other than 8x or 9x, that is, having a digit from 0x to 7x or from Ax to Fx.